I honestly find 4 a really difficult age.
If it has ramped up since 3, I would say you're in grey area territory - it seems anecdotally, children who later turn out to be neurodivergent tend to feel a lot harder at this age, I think because the majority of children tend to grow out of the toddler tantrums and emotional dysregulation by 4 and get better at following instructions, communicating, working with you and managing on their own. Not perfect of course, they are still only little, but there seems to be a significant shift where it's like wow, now they are a little person rather than simply an adorable agent of chaos. But if your child just ramps up the chaos and dysregulation then it can feel a bit like WTF is happening now.
I say grey area because of course some children do simply have their tricky period at 3/4 instead of 2/3, calm down by 5 and don't turn out to be ND but I do think it's useful to have the possibility in mind.
It does help to know if they are ND in the same way that it would help to know if somebody is deaf but excellent at lipreading. If you keep talking to them when they are facing the wrong way, and they don't hear you and you get frustrated and think they are being rude and then by the time you do get their attention you have irritable body language, they are likely to respond to that body language by being irritable back and you will both have a bad impression of each other and it will sour all your interactions. OTOH if you know that the person is deaf, then you know that you need to face them when speaking and you probably will have fewer communication struggles. And if you made an incorrect assumption and the person is not deaf, it's not like making sure you face somebody is a terribly rude thing to do - it can only improve communication.
This is similar to what happens with a lot of ND children. We have an expectation, probably a completely unconscious one that you never even thought of as an expectation, and the ND child can't meet it and this comes across as being rude, or obstinate, or exasperating. We miss pieces of information from them as well. For example, most people would probably understand that a lot of children would struggle to regulate their behaviour in a heatwave and you'd want to make sure they have access to water and shade. But a child who has sensory sensitivities might be feeling as uncomfortable as the NT child in a heatwave but every day. It might be that the noise, light, sensation of clothing etc of everyday life feels as oppressive as this kind of heat to them and yet because it's normal for everyone else, nobody is thinking to offer them breaks from it like a different place to sit in the classroom away from a sunny window, or things which might help like ear defenders or the option to wear non-standard uniform.
If she has always been difficult to settle it could be that there are sensory issues at play. If you ever listen to any interview with Lisa Lloydd (SENbetweeners author/ASD with a G&T on social media) her description of how her children were so difficult to settle as babies and toddlers will probably ring true.
Ignoring it is impossible IME. I did find it was easier to apply parenting advice once I got my own ADHD diagnosed and treated (appreciate this is another huge waiting list and/or you might not even feel this is applicable anyway). Understanding the concept of dysregulation rather than trying to address any specific behaviour did help me a lot. Ultimately reducing the child's dysregulation will reduce the behaviour which then means you're not SO stuck in a constant cycle of dysregulating each other and means you can potentially work on things individually.
It was harder for me with my eldest because I had no clue about ND back then. I did worry intensely about our relationship. He is 16 now and we have a much better relationship. One thing I did was just try to write down each day one nice thing we did together even if it was something stupid like we watched a TV programme together or he showed me a drawing he did at school or we kicked a conker all the way home (there is one stretch where I ONLY wrote this every day for about 2-3 weeks in a row
) I can't remember the specifics of the bad interactions now, but I do remember some of the nice things I wrote down.
One book which helped me with him was When Your Kids Push Your Buttons. It won't stop the behaviour and some parts of it are naff but it helped me see where/why it was winding me up and reframe some aspects.